Arthroscopy is the performance of a surgical procedure within naturally occurring joints through a cannula. The procedure may be simple observation and inspection of tissue structures within the joint, or may involve performing surgical steps through the cannula inserted through soft tissue into the joint capsule. Arthroscopic surgery has become routine and is increasingly being adopted for performing surgery within the human knee and shoulder and is being explored and may be adopted for use in other joints such as the elbow, ankle, wrist, etc. By way of example only, arthroscopy is commonly used in connection with the inspection and repair of the meniscus and ligaments of the knee and inspection and repair of the rotator cuff in the shoulder.
During arthroscopic surgery, multiple cannulas are typically inserted into the joint. One cannula accommodates the arthroscope through which the surgeon may visualize tissue and structures within the joint either directly or by projection of an image onto a monitor or screen. Additional operating cannulas allow the surgeon to approach the tissue within the joint from various angles with appropriate surgical instruments to perform a desired procedure.
In order to create greater visibility and working space, the joint typically is distended during arthroscopic surgery by providing a source of pressurized saline, such that the saline flows or is pumped into the joint to distend the joint and create working space. For example, a saline bag may be elevated to create a pressure head, with the outflow of the bag attached to the insufflation port of one or more of the arthroscopic cannulas. More commonly, a saline fluid pump issued to create a substantially constant fluid pressure. Saline fluid pressure of at least 40 millimeters of mercury is generally required to distend the joint sufficiently for arthroscopic surgery, and pressures of 70 to 80 millimeters of mercury are commonplace during arthroscopic surgery.
During arthroscopic surgery, the surgeon frequently manipulates the various cannulas to view different portions or structures within the joint or to manipulate, cut, remove, suture, staple, anchor or otherwise diagnose and repair conditions within the joint. Such manipulation of the various cannulas creates leverage against surrounding skin, fascia and muscle structures, thereby stretching and loosening such structures as the procedure progresses. During surgery a surgeon may also elect to change cannula diameter at a given entry site, removing a cannula of a first diameter and replacing it with a cannula of a different diameter to accommodate different size instrumentation. Such insertion and removal of the cannula can further contribute to opening of the incision and stretching and loosening of surrounding tissue. As the soft tissue surrounding the cannula stretches and loosens during arthroscopic surgery, pressurized saline within the joint penetrates various layers of tissue surrounding the joint and becomes dispersed through such tissues. The penetration of saline into surrounding soft tissues enlarges the soft tissue surrounding the joint and creates pressure on various tissues and vessels after surgery, prolonging discomfort and recovery time. A build up of saline fluid in the tissue layers surrounding the incision also makes the joint tense, making it difficult to manipulate the joint and instruments to desired angles during surgery. A further potential complication is migration of saline through tissue. By way of example only, if a patient is placed in a lateral position with the arm elevated during shoulder surgery, fluid penetrating tissue layers may migrate along the shoulder toward the neck, and may cause swelling around the neck including critical structures such as the windpipe. Presented with such a situation, a surgeon likely will elect to keep the patient for a longer post-operative period and may require an overnight stay for observation until the saline dissipates and concern about pressure on vital structures such as the windpipe, arteries or veins is reduced. In addition, loosening of soft tissue structures surrounding the arthroscopic cannula permits saline to leak from the joint capsule around the outside of the cannula. Leaking saline flows over the patient and onto the floor of the operating room, creating wet, slippery and undesirable operating conditions. Leakage of saline during arthroscopic surgery has become sufficiently commonplace that arthroscopic surgeons and operating room staff routinely wear waterproof boots in the operating room. In addition, suction equipment is routinely used to collect and remove puddles of leaked saline from the operating room floor. In addition to the inconvenience and safety issues created by puddles of saline, the loosening of tissue surrounding the cannula can also lead to expulsion of the cannula from the joint under the pressure of the saline. Expulsion of the cannula interrupts the procedure, prolonging surgery and exposure of the patient to anesthesia. If expelled with sufficient force, the cannula can also become a projectile, creating a safety hazard to the surgeon and operating room personnel. In addition, if an expelled cannula contacts a non-sterile surface, a replacement sterile cannula and a replacement instrument inserted through the cannula at the time of expulsion must be opened and re-inserted into the joint to continue surgery.
The loss of saline during surgery due to leakage between the cannula and the incision also increases the expense of the procedure as numerous bags of saline are used during the procedure in excess of the actual volume required to distend the joint during surgery. Due to such leakage, it is not uncommon to use three to six bags of saline, and over ten bags in extreme circumstances in an arthroscopic surgical procedure. Most of this saline leaks out of the joint or permeates tissue surrounding the joint. Each bag contains 3,000 cubic centimeters of saline, so several liters of saline may find its way into adjoining tissue or onto the operating room floor.
An arthroscopic cannula with an external thread is known. See for example Glowa U.S. Pat. No. 5,779,697.
Laparoscopic cannulas with anchors, including balloon structures to hold the cannula in place against accidental removal as instruments are inserted and removed, also are known. See for example Shichman U.S. Pat. No. 5,217,441; Yoon U.S. Pat. No. 5,445,615; Orth U.S. Pat. No. 5,836,913; and Hopper U.S. Pat. Nos. 5,697,946 and 6,524,283. The foregoing patents relate to abdominal, i.e., laparoscopic, surgery during which the abdomen is insufflated with carbon dioxide gas. Laparoscopic surgery utilizing gas insufflation does not implicate the considerations identified above with respect to leakage of saline during arthroscopic surgery.